The present invention relates to a cyanoethylpullulan which is a novel high-polymeric compound hitherto not known or not described in any prior art literatures. The invention also relates to the method for the preparation of it. The inventive cyanoethylpullulan has very unique properties and is useful as shaped in films or sheets or as a binder agent in some specific electric applications by virtue of its remarkably high dielectric constant, especially, when the degree of cyanoethylation in 50% or higher.